Sarah Mary Josephine Winstedt (née O'Flynn; 4 April 1886 – 9 September 1972) was an Irish-born physician, surgeon and suffragist. She spent most of the period of 1913–35 in British Malaya, and for her contributions to colonial healthcare she was posthumously inducted into the Singapore Women's Hall of Fame. She served in a medical capacity in both world wars, and was awarded the King George V Silver Jubilee Medal in 1935.
Sarah O'Flynn was born in 1886 in Sixmilebridge, County Clare, to James O'Flynn, a wool miller, and his second wife, Margaret (née O'Halloran). She attended convent schools in Ireland and France and graduated MB ChB from the University of Edinburgh in 1912. She was subsequently appointed an assistant in obstetrics at the Royal Free Hospital in London. During this period, she was also active in the campaign for women's suffrage; she once spent a week on a hunger strike at HM Prison Holloway after attempting to storm parliament with a group of protesters.
In 1913, after attending a course on tropical diseases at the London School of Tropical Medicine, O'Flynn joined the Colonial Medical Service and was sent to British Malaya. There, she ran the women's and children's ward at Kuala Lumpur Hospital and established a new hospital for women and children in the Kuala Pilah District. While the hospital was under construction, she travelled across the countryside by elephant and bicycle to deliver care; these home visits helped to increase trust in Western medicine among the rural population.